John R. Dowdle

A deeply integrated adaptive GPS-based navigator with extended range code tracking

This paper presents a new approach to GPS-based navigation which offers significant improvement in antijam capability over traditional designs. The algorithms may be implemented at low cost in software in existing and future GPS receivers using, as inputs, postcorrelation I and Q data and, optionally, raw data from other sensors. Traditional systems are not optimal at high jammer-to-signal (J/S) ratios as a consequence of modular design, use of traditional fixed-gain or gain-scheduled tracking loops, and use of artificial moding logic. The approach described here employs a nonlinear filter that operates efficiently at all J/S levels. Filter gains continuously adapt to changes in the J/S environment, and the error covariance propagation is driven directly by measurements to enhance robustness under high jamming and dynamics conditions. Extended-range correlation may be optionally included to increase the code tracking loss-of-lock threshold under high jamming scenarios. Computational complexity is comparable to an extended Kalman filter. Results of hardware-in-the-loop simulations are presented which demonstrate improvements of 15 dB or more in antijam capability relative to traditional designs.

An optimal control and estimation algorithm for missile endgame guidance

The design of an optimal guidance and control system for a short range air-to-air missile is undertaken. An optimal target tracking filter is used to track target position and velocity, and a Generalized Likelihood Ratio approach to maneuver detection is employed with maximum likelihood estimation techniques to estimate target acceleration. The estimated target variables are then used with a modified linear quadratic regulator to generate the required guidance commands to minimize miss distance.

Robust estimator design using mu synthesis

H/sub infinity / norm optimization and the structured singular value mu are used to design state estimators that are robust to noise and plant modeling errors. An H/sub infinity / optimal estimator is derived as the solution to a minimax problem. In the suboptimal case, as an H/sub infinity / norm constraint is removed, the minimax estimator approaches the steady-state Kalman filter. Robustness to plant modeling errors is achieved by minimizing a frequency-weighted H/sub infinity /-norm problem. The weighted H/sub infinity / norm, mu , is an upper bound for mu , and therefore provides a sufficient condition for robust performance. The Kalman filter and mu estimator are compared using an example plant with modeling uncertainty. The mu estimator has slightly worse performance than the Kalman filter for the nominal plant model, but, unlike the Kalman filter, maintains its performance over the entire range of the modeling uncertainty.<<ETX>>

A Nonlinear Code Tracking Filter for GPS-Based Navigation

Current Global Positioning System (GPS)-based navigation systems are highly susceptible to unintentional and intentional jamming due to relatively low signal power at the receiver antenna and, in part, due to suboptimal code tracking loop designs that do not account for measurement nonlinearities near loss-of-lock. A nonlinear code tracking filter is developed whose architecture is based on a rigorous minimum-variance solution of the navigation problem, rather than using prespecified tracking loop architectures. The filter implementation can be viewed in terms of the classical notions of error detector functions, which depend on signal-to-noise ratio (SNR) and root mean square (rms) code tracking error. Detector functions are defined for both code tracking error and code tracking error variance. The filter responds more rapidly than current designs to rapidly varying jammer power due to a measurement-dependent term in the covariance calculations. Extended-range tracking is utilized, yielding linear state vector error detector functions (i.e., the filter is essentially optimum) out to the maximum allowed by the correlator range, and reducing the need for reacquisition. Significant antijam improvements relative to current designs are predicted from high-fidelity simulation and hardware demonstrations. Computational requirements are comparable to extended Kalman filter/vector tracking loop techniques.

An integrated approach to the guidance and control of tactical missiles

The guidance and control problem for tactical air-to-air missiles is addressed using a modern control theory approach. The autopilot is designed based upon a generalized formulation of the optimal tracker to provide both airframe stability and command following from the guidance signals, and the guidance law is designed using the optimal regulator. Associated implementation issues are discussed.

Submeter navigation grid system concept

This paper describes a concept for a system that provides the capability for accurate targeting and weapon delivery within a prescribed geographic context. This system, entitled submeter navigation grid, defines a geographic region that enables targeting platforms to perform relative navigation to the centimetre level. Ultimately, targeting information is delivered to an appropriate tactical platform, and the system enables precision guidance of this platform to the identified target coordinates. The submeter navigation grid consists of both airborne and land based components with communications links between them. Of note is that the submeter navigation grid utilizes a pseudo-lite as an electronic counter-counter measure against a potential jamming threat.

APPLICATION OF MULTIVARIABLE DESIGN TECHNIQUES TO ROBUST CONTROL OF A LARGE-SCALE SYSTEMS

Reducing plant order consequently introduces unmodeled Typical issues and tradeoffs resulting from dynamics into the system, which must then be application of various modern multivariable controller accounted for via stability and performance robustness design techniques to large-scale systems are illustrated considerations. Additionally, parametric errors in the herein by synthesis of robust H2 optimal, H,optimal, open-loop system model invariably exist, and their and H.. loop-shaped compensators for a space-based laser effects must be considered. The lightly damped nature of bearmr control example problem using reduced-order typical large-scale systems is also a design issue of models. A design framework is adopted which allows concern, leading to extremely slow oscillatory transient stability robustness in the presence of resulting responses, and, due to the location of lightly damped poles near the complex plane imaginary-axis, potential neglected dynamics to be guaranteed via unstructured uncertainty representation and the Small Gain Theorem,n obtaining closed-loop stability andor and performance robustness to be independently verified. Infinity-norm bounds on two closed-loop transfer nfunctions provide the key figures-of-merit foer This paper addresses several of the above issues in functions provide the key figures-of-merit for the context of multivariable feedback design for a chosen guaranteeing the desired stability robustness and nominal context of muluvaable feedback design for a chosen performance conditions. A final design is obtained example problem. The results presented in this paper performance conditions. A final design is obtained which is verified to meet nominal performance st control ofinuing research effort focusing on specifications, and is also seen to possess robustness of robust control of large-scale systems. Previous both stability and performance to dynamics truncated in researchl discussed mode ultivaiable design the model reduction process. The effects of open-loop methodologies, and addressed possible application t pole parametric uncertainty are also examined, the main primary mirror beam jitter control of a space-based laser result observed being a severe degradation in closed-loop (SBL). In a subsequent work 2, H, optimization and system performance. reduced-order models were employed to perform requirements analysis for the combined beam jitter and

Dissipativity Methods for Multivariable Control System Analysis

This paper examines the utility of dissipativity concepts in the analysis of stability and the robustness of stability of linear control systems. It is shown that dissipativity concepts may be used to generate many previously known results related to the robustness of stability.